Method of increasing the meltblown jet thermal core length via hot air entrainment

Abstract

A method for producing super fine meltblown fibers increases the length of the meltblown jet thermal core to increase the dwell time of the extruded thermoplastic polymer within the jet thermal core. Through use of the method it is practical to use low viscosity resins and further to provide meltblown nonwovens with superior barrier properties to the passage of fluids and particularly gases. The method further provides a useful means for blooming internal additives to the surface of the fibers.

We claim:  
     
       1. A method of increasing a meltblown jet thermal core length issuing from a melt blown die, comprising: 
       adding heat energy to the jet thermal core during initial formation of the jet thermal core to shroud the jet thermal core from ambient air thereby increasing the jet thermal core length and attenuation time of the meltblown fibers.  
     
     
       2. The method of increasing a meltblown jet thermal core length issuing from a melt blown die according to  claim 1 , further comprising: 
       entraining hot air during initial formation of the jet thermal core of between 100° F. and 400° F. at an air flow rate of at least about 500 feet/minute from a source below the meltblown die knife edge towards the area occupied by the meltblown jet thermal core.  
     
     
       3. The method of increasing a meltblown jet thermal core length issuing from a melt blown die according to  claim 2 , further comprising: 
       entraining hot air during initial formation of the jet thermal core of at least 300° F. from a source below the meltblown die knife edge towards the area occupied by the meltblown jet thermal core.  
     
     
       4. A method of producing a meltblown nonwoven web comprising: 
       extruding a thermoplastic polymer in its liquid state into a meltblown jet thermal core;  
       creating a zone of hot air around the meltblown jet thermal core to enable the jet thermal core to lengthen thereby increasing fiber formation dwell time within the jet thermal core at temperatures above the extrudate melting point and extending an attenuation time of fiber formation resulting in fine meltblown filaments; and  
       collecting the filaments on a collection surface to form a nonwoven web.  
     
     
       5. The method of producing a meltblown nonwoven web according to  claim 4  further comprising entraining air in a range of about 100° F. to 400° F. from a source below the meltblown die knife edge towards the area occupied by the meltblown jet thermal core. 
     
     
       6. The method of producing a meltblown nonwoven web according to  claim 4  further comprising entraining air in a range of about 200° F. to about 400° F. at a rate of between about 500 and 1000 feet/minute from a source below the meltblown die knife edge towards the formation area of the meltblown jet thermal core. 
     
     
       7. The method of producing a meltblown nonwoven web according to  claim 4 , further comprising: 
       lengthening the jet thermal core length to a distance increase of between 11% and 142% with a centerline temperature of at least 90% of the jet thermal core formation temperature.  
     
     
       8. The method of producing a meltblown nonwoven web according to  claim 4  further comprising selecting the polymer to have a melt flow range between 400 and 1500 grams/10 minutes. 
     
     
       9. The method of producing a meltblown nonwoven web according to  claim 4  further comprising using a low viscosity polymer having a melt flow rate at or below 1500 grams/10 minutes. 
     
     
       10. The method of producing a meltblown nonwoven web according to  claim 4  further comprising using a low viscosity polymer having a melt flow rate at or below 400 grams/10 minutes. 
     
     
       11. The method of producing a meltblown nonwoven web according to  claim 4  further comprising selecting the fibers to be comprised of polypropylene polymer. 
     
     
       12. The method of producing a meltblown nonwoven web according to  claim 4  further comprising producing fibers of less than 2 microns diameter to form the web. 
     
     
       13. The method of producing a meltblown nonwoven web according to  claim 9  wherein the web has an air permeability at or below 70 SCFM per square foot. 
     
     
       14. The method of producing a meltblown nonwoven web according to  claim 10  wherein the web has an air permeability at or below 70 SCFM per square foot. 
     
     
       15. The method of producing a meltblown nonwoven web according to  claim 9  wherein the web has a “basis weight” of 0.5 osy and an air permeability rate of below 125 SCFM/square foot. 
     
     
       16. The method of producing a meltblown nonwoven web according to  claim 10  wherein the web has a “basis weight” of 0.5 osy and an air permeability rate of below 125 SCFM/square foot. 
     
     
       17. The method of producing a meltblown nonwoven web according to  claim 9  wherein the web has a “basis weight” of 0.5 osy and a hydrohead of at least 112 mbars. 
     
     
       18. The method of producing a meltblown nonwoven web according to  claim 10  wherein the web has a “basis weight” of 0.5 osy and a hydrohead of at least 112 mbars. 
     
     
       19. The method of producing a meltblown nonwoven web according to  claim 9  wherein the web has a “basis weight” of 0.5 osy and a hydrohead of between 112 and 139 mbars. 
     
     
       20. The method of producing a meltblown nonwoven web according to  claim 10  wherein the web has a “basis weight” of 0.5 osy and a hydrohead of between 112 and 139 mbars. 
     
     
       21. The method of producing a meltblown nonwoven web according to  claim 4  wherein the jet core is lengthened to bloom polymer additives to the surface of the fiber.